This presentation is the aftermath of a laboratory experiment to understand the refrigeration cycles and functions in detail. It also shows the various uses and modifications refrigeration system accounts to.
A Presentation on
STUDY OF A REFRIGERATION UNIT
Muhammad Shafiul Munir
Student ID: 0902049
A2 (Group 04)
Department of Chemical Engineering, BUET
Presentation at a Glance
What is Refrigeration
Vapour- Compression Refrigeration Cycle
Why we are so concerned about Refrigeration
Thermodynamic Significance of Refrigeration
What is Refrigeration ??
Transfer of heat from a
region from a higher one
The device that works
cyclically to perform this
job is Refrigerator
The working fluid used in
refrigerator is called
Ideal Vapour Compression Cycle
1. (1-2) Isentropic
Compression in a
2. (2-3) Constant Pressure
Heat Rejection in a
3. (3-4) Throttling in an
4. (4-1) Constant Pressure
Heat Absorption in an
The Actual Vapour Comoression Cycle
• Fluid Friction
• Heat Transfer
Why Study Refrigeration ??
Used in Oil
Why Study Refrigeration (Continued) ??
Steel and Cutlury
Meats, Fish and
1. Rate of Heat Transfer in both Evaporator and Condenser-
2. Overall Heat Transfer Co-efficient for both Evaporator and
U= Q/ AΔt LMTD
3. Compressor Pressure Ratio-
Rate of Heat
Over all Heat
( Pc / Pe)
01 20.5 41.8 52.25 375.8 10.77
02 167.2 41.8 435.78 529.7 10.49
03 12.54 83.6 31.75 1435.4 10.45
04 83.6 125.4 227.37 1810.9 11.41
05 41.8 125.4 104.5 1810.9 11.55
Graph 01: Saturation Pressure Vs. Saturation Temperature
0 20 40
Graph 02: Heat Transfer Rate Vs. Condensing Temperature
20 25 30
Heat Transfer Rate Vs.
Graph 03: Heat Transfer Rate Vs. Compressor Pressure Ratio
10 11 12
Compressor Pressure Ratio
Heat Transfer Rate Vs.
Compressor Pressure Ratio
Refrigeration- Thermodynamic Point of View
Refrigeration operates on
a true Thermodynamic
Nucleate Boiling and
Steady Flow processes like
and Heat Exchange.
In this experiment our main objective was to study
After the Experiment it is quite clear that the
objectives were quite fulfilled.
Performance of refrigeration can be increased using-
Cascade Refrigeration System
Multistage Refrigeration System
Assalamu Alaikum, Good evening Honourable Teachers, I Muhammad Shafiul Munir am Thanking for giving me the floor to present on the experiment entitled ‘Study of a Refrigeration Unit’. I conducted the experiment along with my partners from A2 Group 04 student id of 0902046, 47, 48 and 50.
Now I want to provide a general overview about the presentation, at first I will be describing what is refrigeration and how it works and Experimental Set-up, Procedure, graphs and Result and discussion will be following one after another.
Now, let’s first see what is refrigeration? It’s basically defined as heat transfer from a lower temparature zone to a higher one. The device which is appointed to do the task is called a refrigerator, which operates cyclically using a working fluid called refrigerant.
Here, the simplest mechanism of refrigerator is shown, it’s taking QL amount of heat from cold refrigeration space at a lower temparature TL and rejecting Qh amount of heat into a highe temparature Th, where Wnet is the net work input.However, from the first law of thermodynamics we clearly know that energy can neither be created nor destroyed, heat taken must be dissipated to the surroundings, and from Classius’s statement of Second law of thermodynamics we know that ‘heat will not pass from a cold to a hotter region without external aid’, so refrigerator definitely needs an input of high grade enerygy to operate. Hence, a refrigerator normally uses a work input and operates on the vapour compression cycle.
This is an ideal vapor compression cycle on which the refrigerator is supposed to operate. The work input to the ideal vapor compression cycle drives a compressor which maintains a low pressure in an evaporator and a higher pressure in condenser. As the temperature at which a liquid evaporates or condenses is dependent on pressure, if a suitable refrigerant is introduced it will evaporate at a low temperature in the low pressure evaporator and will condense at a higher temperature in high pressure condenser.
The high pressure liquid formed in the condenser must then be returned to the evaporator at a controlled rate through a throttling device.
A compressor uses work input to reduce pressure in evaporator and increase pressure of vapor transffered to Condenser.
A condenser where the high pressure vapor condenses, rejecting heat to it’s surroundings.
A flow control device ( throttling valve) which controls the flow of liquid back to the evaporator and which brings about the pressure reduction...
An evaporator where heat is taken in at a low temperaure as a liquid evaporates at a low pressure.
An actual vapour-compression refrigeration cycle differs from the ideal one in several ways, owing mostly to the irreversibility that occurs in various components. Two common sources of irreversibility are fluid friction (causes pressure drops) and heat transfer to or from the surroundings.
In the ideal cycle, the refrigerant leaves the evaporator and enters the compressor as saturated vapour. In practice, however, it may not be possible to control the state of the refrigerant so precisely. Instead, it is easier to design the system so that the refrigerant is slightly superheated at the compressor inlet. This slight overdesign ensures that the refrigerant is completely vaporized when it enters the compressor. Also, the line connecting the evaporator to the compressor is usually very long; thus the pressure drop caused by fluid friction and heat transfer from the surroundings to the refrigerant can be very significant.
The compression process in the ideal cycle is internally reversible and adiabatic, and thus isentropic. The actual compression process, however, involves frictional effects, which increase the entropy, and heat transfer, which may increase or decrease the entropy, depending on the direction.
In the ideal case, the refrigerant is assumed to leave the condenser as saturated liquid at the compressor exit pressure. In reality, however, it is unavoidable to have some pressure drop in the condenser as well as in the lines connecting the condenser to the compressor and to the throttling valve. Also, it is not easy to execute the condensation process with such precision that the refrigerant is a saturated liquid at the end, and it is undesirable to route the refrigerant to the throttling valve before the refrigerant is completely condensed. Therefore, the refrigerant is sub-cooled somewhat before it enters the throttling valve. We do not mind this at all, however, since the refrigerant in this case enters the evaporator with a lower enthalpy and thus can absorb more heat from the refrigerated space. The throttling valve and the evaporator are usually located very close to each other, so the pressure drop in the connecting line is small.